It is known to use power steering in road vehicles, e.g. electrical power assisted steering, commonly abbreviated as EPAS, in a road vehicle such as a car, lorry, bus or truck, wherein an electric motor assists a driver of the road vehicle by adding an assistive torque to e.g. a steering column or steering rack of the road vehicle.
It is further known to use advanced driver assistance systems, commonly abbreviated as ADAS, such as Lane Keeping Aid systems, commonly abbreviated as LKA systems, in order to help a road vehicle driver maintain the road vehicle in a desired lane. For LKA or lane centering systems where an EPAS is used, a steering wheel torque overlay, i.e. additional steering wheel torque on top of what would have been obtained by the base assist of the EPAS, is used for lateral position control.
However, the need for more advanced autonomous steering functions has put new requirements on current steering safety concepts. One example of such is commonly called Pilot Assist, commonly abbreviated as PA, which helps a driver to drive the vehicle within the road lane whilst at the same time maintaining a preselected time interval to a preceding vehicle.
Current safety mechanisms for driver assistance functions, such as PA functions, commonly rely on a driver to always hold his or her hands on the steering wheel. By holding the steering wheel, the comfort of the driver will be influenced by any torque disturbances in the steering system.
A Steer Torque Manager, commonly abbreviated as STM, is a component that includes a Driver In the Loop functionality, commonly abbreviated as DIL functionality, and a wheel angle controller. The DIL functionality usually relies on a torsion bar torque sensor to decide when and how to hand over control to the driver from the Pilot Assist- or Lane Keeping Aid-functionality and when the driver is to be treated as a disturbance that needs to be suppressed by the wheel angle controller. The DIL-functionality hands over control to the driver by limiting the torque output of the wheel angle controller, e.g. by scaling the output or by decreasing the maximum and minimum allowed overlay torque. The STM is commonly located in an EPAS supplier node, herein referred to as Power Steering Control Module, commonly abbreviated as PSCM.
Since a driver is required to keep his or her hands on the steering wheel the overall comfort and customer value of the PA functionality is largely decided by the STM, and in particular the wheel angle controller thereof. Advanced driver assistance systems, such as the above described Pilot Assist, adds a requirement of high bandwidth in the wheel angle controller in order for a PA path wheel angle request to be tracked accurately and not having a sluggish tracking performance of the PA path wheel angle request with the potential of causing car sickness, which a decreased bandwidth potentially would incur.
However, high bandwidth may result in pulsating torque sensations in the steering wheel, potentially causing discomfort to a driver holding on to the steering wheel.
Thus, the requirement of high bandwidth is contradictory because this requirement has the potential of causing discomfort to a driver by the resulting pulsating torque sensations in the steering wheel while a decrease in bandwidth when using advanced driver assistance systems, such as the above described Pilot Assist, has the potential of causing discomfort to a driver and other vehicle occupants by causing car sickness.
Thus, there is a need for improved solutions which are able to comfortably handle the above whilst facilitating fulfilment of high Automotive Safety Integrity requirements.